This competitive renewal application will continue examining the molecular mechanisms by which nickel compounds mediate lung carcinogenesis. In particular, this proposal seeks to identify the molecular mechanisms linking nickel-induced lung sustained inflammation to tumorigenicity of human bronchial epithelial cells (HBECs) in vitro and in vivo. Although there is an association between nickel- induced sustained airway inflammation and lung cancer development, the molecular mechanisms linking nickel exposure to the sustained lung chronic inflammation are not understood yet. The studies obtained from the last funding period and preliminary studies demonstrate that nickel exposure results in the activation of the nuclear factor-?B (NF?B), which in turn mediates COX-2 induction. Our studies also show that nickel exposure enables activation of AP-1, which in turn mediates TNF-? induction. Furthermore, we find that TNF-? enables COX-2 induction through the NFAT-dependent pathway. In addition, we find that there is crosstalk between the NFAT and NF?B pathways during cellular response to nickel exposure. Thus, the main hypothesis of this renewal proposal is that the NFAT/ NF?B activation and the pro-inflammatory TNF-? and COX-2 induction will form positive inflammatory feedback loops, which are responsible for the formation and maintenance of sustained chronic lung inflammation and the induction of lung epithelial cell tumorigenicity due to nickel exposure. We propose the following Specific Aims: 1), To test the hypothesis that the inflammatory positive feedback loops being formed by NF?B, NFAT, and TNF? are responsible for the maintenance of sustained COX-2 induction due to nickel exposure in HBECs; 2), To determine the role of the positive inflammatory feedback loops in the development of tumorigenicity induced by nickel exposure in HBECs.; 3), To assess the central role of TNF-? in nickel-induced chronic lung inflammation and its mechanisms in vivo. The overall goal of this proposal is to clarify the formation of positive inflammatory feedback loops among NFAT, NF?B, TNF-? and COX-2, in nickel exposure both in vitro and in vivo, and to determine the role of the positive inflammatory feedback loops in nickel-induced HBECs' tumorigenicity, as well as the central role of TNF-? in the maintenance of lung sustained chronic inflammation and lung carcinogenesis during nickel exposure in vivo. Success of the proposal will facilitate our understanding of the molecular mechanism(s) that lead to the formation and maintenance of a lung chronic inflammatory microenvironment, and its role in lung carcinogenesis due to nickel exposure. A better understanding of these issues may provide valuable information for the designing of more effective agents for the prevention and therapy of lung cancers. We believe that the proposed contribution of positive inflammatory feedback loop responsible for nickel-induced lung tumorigenicity is novel.